Aqueous emulsion of a silicone rubber resin has been known in the art, and various products are on the market including those intended for the cosmetic preparation. However, almost all such commercially available products for the application of cosmetic preparation are silicone rubber resins emulsified and dispersed in water by using a silicone oil or the like, and these products can not be regarded as a product in an aqueous system. JP-A H10-175816 discloses the system wherein silicone rubber particles are synthesized, dried, and again emulsified and dispersed, and this process requires the steps of drying and emulsification in addition to the step of the polymerization. Another known products are aqueous dispersions of the silicone rubber by addition reaction of a hydrogen polysiloxane and a vinyl polysiloxane. These products, however, tend to undergo separation, and because of such separation, almost all of these aqueous dispersions were used in the form of powder after separation and they were rarely used in the cosmetic preparation in the form of an aqueous dispersion. In another method, the silicone rubber produced, for example, by solution polymerization is dissolved again in a silicone oil, and then subjected to mechanical emulsification (JP-A H08-245881). This method is economically disadvantageous.
Silicone emulsions capable of forming a film by crosslinking have also been disclosed in JP-A 2007-51236, and these products are in the market since their high strength and softness as well as water repellency were highly evaluated. These are products prepared by simple emulsion polymerization using a siloxane for the starting material, and thus economically advantageous. These products, however, contained surfactants and acids unsuitable for cosmetic products.
JP-A H11-71522 discloses a polyorganosiloxane emulsion prepared by emulsion polymerization of a silanol group-endcapped polydiorganosiloxane in the presence of (B) an unsaturated aliphatic sulfonate and/or sulfonate methyl hydroxide formed in the reaction system of a sulfonate salt and an acid and (C) water. This polyorganosiloxane emulsion, however, uses sulfuric acid, hydrochloric acid, formic acid, and sulfonic acid in its production. These acids are mostly strong acids under the restriction of Poisonous and Deleterious Substances Control Act and other laws, and their use in the application of cosmetic preparation is unsuitable. Formic acid which is not a strong acid is also under the restriction of Poisonous and Deleterious Substances Control Act as a deleterious substance when used at a high concentration, and its use in the application of cosmetic preparation is also unsuitable.
JP-B S44-20116 discloses an emulsion polymerization method of an organosiloxane and a silanol group-containing disilcarbane in an aqueous medium in the presence of a sulfonic acid catalyst having surfactant activity selected from benzene sulfonic acid substituted with an aliphatic hydrocarbon group, naphthalene sulfonic acid, aliphatic hydrocarbon sulfonic acid, and silylalkylsulfonic acid, which is most typically an alkylbenzene sulfonic acid such as dodecylbenzene sulfonic acid. However, these are silicone oils, and they are used in a manner clearly different from the silicone rubber. As in the case of literatures as described above, the acid used is a strong acid which is unsuitable for use in the application of cosmetic preparation.
Such polymerization also inevitably involves use of an anionic surfactant such as sodium laurylsulfate or sodium laureth sulfate. However, these compounds, are irritant and under the restriction of Law concerning Pollutant Release and Transfer Register (hereinafter also referred to as PRTR). Also, these compounds may be toxic to human and environment (aquatic life), and accordingly, they are not suitable as a material used in cosmetic preparations.
In addition, properties such as high spreadability, lighter texture, and softer touch are expected for a preparation used in cosmetic applications.